With the Moffat Tunnel being built, it was clearly necessary to connect the west end of the D&SL to something, lest the tunnel become a big, expensive hole to, essentially, nowhere... One option was to complete the building of the D&SL westward to its other namesake city. This would have required nearly three hundred miles of new railway. However, there was another option....

Aside from avoiding yet another mountain crossing and potential helper district, one of the reasons that the Denver, Northwestern & Pacific had chosen the route through Gore Canyon to McCoy was to provide the possibility of a short linkage with the Rio Grande. Following along the Grand (now Colorado) River canyon west from Bond, CO, it was only a short 45 water-level miles over to a point on the Rio Grande's standard gauge mainline near the confluence of the Grand (Colorado) and Eagle Rivers. Freight could then be sent west over the D&RGW to Salt Lake and, via sister road Western Pacific, the West Coast. Clearly this connector was far more practical than completing Moffat's dream of a railroad west from Craig, this would complete the line to Salt Lake with a minimum amount of work. This was clearly the better option. This new piece of railway would connect two points, Dotsero or Orestod (yes, the names are perfect reversals of each other), and be known as the Dotsero Cutoff.

Despite the D&SL and the D&RGW having jointly chartered the Denver, Salt Lake & Western to build the cutoff in 1924, little happened until after the Moffat Tunnel's completion. The connection was initially just obvious for the D&SL - the additional bridge traffic it would pick up from the UP's Wyoming line and the Rio Grande's Tennessee Pass main would more than pay for the connection. However, all was not well - there was no real source of funding yet, and the Interstate Commerce Commission was concerned that a D&SL - D&RGW combination would eventually work to eliminate the Tennessee Pass line entirely. The ICC finally agreed that the D&SL would build the cutoff, and the D&RGW would assume ownership. A year or two later, however, both roads found it to be against their best interest - the D&SL now felt that insufficient traffic would surface to justify it, and now the Rio Grande feared it would eliminate revenues from haulage via Tennessee Pass and Pueblo. Thus, neither road acted, and by 1928 when the tunnel was completed, there was absolutely no sign that either road was starting, or would ever start the Dotsero Cutoff.

In 1930, after the Rio Grande petitioned the ICC to gain control of the D&SL, they agreed with one firm condition - the Cutoff must be started within six months and finished within two years. Seeing all the pieces for a competitive transcontinental route in place but not being finished bothered the ICC, and they agreed to this to force action on the Cutoff. In 1932, the D&RGW secured financing through the US government, and Cutoff construction began in November. On 15-Jun-1934, just a few months ahead of the two year deadline, the route was complete. This was really the moment when the modern Rio Grande system mainline was completed - all the major pieces were in place.